1. Field of the Invention
The present invention relates to a multifunctional or multi-frequency quartz crystal unit in which a tuning fork type quartz crystal blank and a quartz crystal blank of thickness-shear mode are hermetically encapsulated in the single same container, and more particularly, relates to a multifunctional crystal unit using a crystal blank of AT cut as a thickness-shear mode crystal blank, and a method of manufacturing the same.
2. Description of the Background Arts
A quartz crystal unit is incorporated in an oscillator or an oscillating circuit as a reference source of frequency and time, and is accommodated in various kinds of electronic apparatuses. A number of such apparatuses accommodates different kinds of crystal units in response to the uses. For example, in small mobile electronic apparatuses including recent portable telephones, a thickness-shear mode crystal unit of AT cut, which generates communication frequency signals, and a tuning fork type crystal unit, which generates clock signals are separately accommodated. The separate accommodation of a plurality of crystal units inhibits the electronic apparatuses from being downsized, and accordingly for example, in Japanese Laid-open Patent Application No. 2000-349181 (JP 2000-349181A), there has been proposed that both of different kinds of crystal blanks are encapsulated in a common container or vessel for the miniaturization purpose.
An example of the conventional multifunctional crystal unit accommodating therein a plurality of crystal blanks of such different vibration modes is illustrated in FIGS. 1 and 2.
As illustrated in FIG. 1, the crystal unit houses two kinds of crystal blanks 2 and 3 in substantially rectangular parallelepiped container 1 for surface mounting. Container 1 is constructed of laminated ceramics to have a recess formed from its upper face, and as illustrated in FIG. 2, container 1 is formed, at four corners of its outer bottom face, with mounting electrodes 4a, 4b, 5a and 5b used for connection with external circuits. Mounting electrodes 4a, 4b, 5a and 5b are formed so as to be somewhat extended and to rise up on the side faces of container 1. In the recess of container 1, stepped portions are formed. On the upper face of container 1 along the periphery of the recess, for example, metallic ring 6 is mounted to which metallic cover 7 is bonded by seam welding, and hereby crystal blanks 2 and 3 are hermetically encapsulated in container 1.
As illustrated in FIG. 3A, crystal blank 2 is a tuning fork type crystal blank which is made of quartz crystal plate of X cut and has vibration mode of length-width-flexure mode, and consists of a fork base portion 8 and a pair of fork arms 9a and 9b. Respective fork arms 9a and 9b of a columnar shape have four faces in which electrically paired excitation electrodes 10 are provided. Further, on both end portions of fork base portion 8 are provided extending electrodes 11a and 11b, so that respective excitation electrodes are extended to extending electrodes 11a and 11b. Extending electrodes 11a and 11b are fixedly bonded by conductive adhesive 12 to a pair of terminal electrodes (not illustrated) formed in the bottom face of the recess of container 1 so as to provide therebetween electrical and mechanical connection. Thus, tuning fork type crystal blank 2 is held within the recess of container 1, so that the plate face thereof is directed vertically. The pair of terminal electrodes to which tuning fork type crystal blank 2 is connected, are electrically connected to the above-described mounting electrodes 5a and 5b through conductive patterns and via-holes formed in the inner face of container 1.
On the other hand, crystal blank 3 of AT cut is a planar plate like crystal blank acquired by being cut out of a quartz crystal by means of AT cut, and has both principal planes in which paired excitation electrodes 13 are formed. Further, crystal blank 3 formed in a rectangular shape has one side formed, at its opposite ends, with a pair of extending electrodes 14a and 14b to which the pair of excitation electrodes 13 are extended, respectively.
In the stepped portion of the recess of container 1 are formed a pair of terminal electrodes (not illustrated) to which extending electrodes 14a and 14b are fixedly bonded by means of conductive adhesive 12 to establish electrical and mechanical connection between the electrodes. Thus, crystal blank 3 of AT cut is held within the recess of container 1 in a manner such that the plate face is directed in a vertical direction. Crystal blank 3 of AT cut is disposed above tuning fork type crystal blank 2. The pair of terminal electrodes to which crystal blank 3 of AT cut is connected are electrically connected to the above-described mounting electrodes 4a and 4b, respectively, through conductive patterns and via-holes formed in the inner face of container 1.
In the described multifunctional crystal unit, tuning fork type crystal blank 2 vibrates at dozen kiloheltz to generate a reference frequency signal for clock use, while crystal blank 3 of AT cut vibrates at several through dozen megaheltz for generating communication frequency in a communication apparatus. For example, when this crystal unit is employed for a cellular telephone, the crystal unit is mounted on a printed wiring board of the cellular telephone, so that mounting electrodes 5a and 5b are connected to an oscillating circuit for clock signal, and mounting electrodes 4a and 4b are connected to an oscillating circuit for communication frequency use. Thus, tuning fork type crystal blank 2 is used as a crystal unit operating at a kilohertz band, while crystal blank 3 of AT cut is used as a crystal unit operating at a megaheltz band.
As described above, when different kinds of crystal blanks are housed in the same container for the surface mount use to be used as two kinds of crystal units, the size of the whole crystal unit can be kept small. Therefore, when this type of multifunctional crystal unit is employed, it is possible to miniaturize electronic apparatuses such as cellular telephones.
In the multifunctional crystal unit of the above-described constitution, when tuning fork type crystal blank 2 and crystal blank 3 of AT cut are respectively mounted to be held in the recess bottom and the stepped portion of container 1, the respective vibration frequencies must be adjusted. Namely, after when conductive adhesive 12 is thermally hardened to fixedly bond tuning fork type crystal blank 2 to the bottom portion of the recess, either the tip ends of fork arms 9a and 9b are cut off, for example, by machining, or metallic films provided at the tip ends of tuning fork arms 9a and 9b are removed away by, for example, laser processing, to adjust the vibration frequency. Then, after the adjustment of tuning fork type crystal blank 2, crystal blank 3 of AT cut is held at the stepped portion by means of conductive adhesive 12, and for example, ion beam is radiated to excitation electrodes 13 of crystal blank 3 so as to reduce film thickness of excitation electrodes 13 thereby adjusting the vibration frequency thereof. After the completion of the adjustment of the vibration frequencies, the common metallic cover 7 is attached so as to close the recess, and the manufacture of the crystal unit is completed.
In the described crystal unit, during the adjustment of the vibration frequency of crystal blank 3 of AT cut, metallic dusts scatting from excitation electrodes 13 might attach to tuning fork type crystal blank 2 to cause a problem such as, for example, a change in the vibration frequency and the short-circuiting between excitation electrodes 10 of tuning fork type crystal blank 2, resulting in an occurrence of defective. Although it might be possible to adopt an alternate way such that the crystal blank of AT cut is placed in the bottom portion of the recess, and the tuning fork type crystal blank is held at the stepped portion, an occurrence of defective due to similar generation of metallic dusts might not be avoided.
Furthermore, since tuning fork type crystal blank 2 and crystal blank 3 of AT cut are housed within the same container, these crystal blanks 2 and 3 are simultaneously driven to obtain both clock signals and communication frequency signals, and as a result problems set forth below might occur: Since respective crystal blanks (crystal units) 2 and 3 form oscillation closed loops together with the associated oscillating circuits, respectively, high frequency currents must flow from the oscillating circuits, and such high frequency currents from the respective oscillating circuits further flow through crystal blanks 2 and 3, and the circuit patterns including their connected mounting electrodes 4a, 4b, 5a and 5b. Therefore, electromagnetic wave leaks out of respective crystal blanks 2 and 3 as well as the circuit patterns to jump into the associated ones to thereby cause mutual interference. As a result, a problem occurs such that the oscillating operation is made unstable. For example, when crystal unit of AT cut generates a communication frequency f0 (for example, 12 MHz), and when tuning fork type crystal unit generates a clock signal (at, for example, 32 kHz), a component of the clock signal is superposed onto the signal of communication frequency, and as a result, phase noise at f0xc2x132 kHz increases in the communication frequency signal.
In particular, mutual interference between excitation electrodes 10 and 13 of respective crystal blanks 2 and 3 having a large area, respectively, could become an unignorable problem. The more miniaturization of a surface mounting type crystal unit is promoted due to a reduction in the height as well as the planar face size of the crystal unit, the larger an adverse influence on the performance of the crystal unit due to the mutual interference will become.
An object of the present invention is to provide a multifunctional crystal unit provided therein with a tuning fork type crystal blank and a thickness-shear mode crystal blank and that is capable of ensuring the oscillating operation by preventing any electrical mutual interference between either the crystal blanks or other constituents.
Another object of the present invention is to provide a multifunctional crystal unit provided therein with a tuning fork type crystal blank and a thickness-shear mode crystal blank and that is improved in its productivity by preventing metallic dusts and the like from attaching to the crystal blanks during the adjustment of vibration frequency of the respective crystal blanks.
A further object of the present invention is to provide a method of manufacturing a multifunctional crystal unit provided therein with a tuning fork type crystal blank and a thickness-shear mode crystal blank, which method can be one capable of improving the productivity of the multifunctional crystal unit by preventing any metallic dusts from attaching to the crystal blanks during the adjustment of vibration frequency of the respective crystal blanks.
In accordance with a first aspect of the present invention, there is provided a multifunctional crystal unit in which a plurality of crystal blanks are hermetically encapsulated in the same container provided with a container body having a recess formed therein, and a cover, wherein the crystal unit is characterized in that respective of the crystal blanks are held in different spaces, and the different spaces are isolated from each other by a shielding member to thereby provide electrical shielding between the crystal blanks.
In accordance with a second aspect of the present invention, there is provided a multifunctional crystal unit in which first and second crystal blanks are housed in a closed container provided with a container body and a cover, wherein the crystal unit is characterized in that the container body has a cross-section of a H-letter shape and recesses formed in both primary planes thereof, while encapsulating in one recess the first crystal blank, and in the other recess the second crystal blank so that the respective recesses are sealed, respectively, by the connection of a cover, either one of the recesses having, at an end face thereof, mounting electrodes.
In accordance with a third aspect of the present invention, there is provided a method of manufacturing a crystal unit, which comprises providing a container body having a cross section thereof in the shape of a H-letter, recesses formed in both primary planes thereof; and mounting electrodes arranged in an end face of either one of the recesses, encapsulating a first crystal blank in one recess in the both primary planes and a second crystal blank in the other recess, adjusting vibration frequencies of the first and second crystal blanks, and thereafter sealing the recesses in both primary planes of the container body with respective covers.